Catheters are being used increasingly as a means for delivering diagnostic or therapeutic agents to internal target sites, and to perform mechanical functions on vasculatures that can be accessed through the circulatory system. For example, in angiography, catheters are designed to deliver a radiopaque agent to a target site within a blood vessel, to allow radiographic viewing of the vessel and blood flow characteristics near the release site. For the treatment of localized disease, such as solid tumors, catheters allow therapeutic agents to be delivered to the target site at a relatively high concentration, with reduction in drug delivery to nontarget sites. Methods for producing localized vasoocclusion in target tissue regions, by catheter injection of a vasoocclusive agent, have been described (coowned U.S. patent application for "Hyperthermic Treatment of Tumors," Ser. No. 751,605, filed July 2, 1985).
Often the target site which one wishes to access is in a tissue, such as brain, liver or kidney, which requires catheter placement along a tortuous path through small vessels or ducts, such as arterial vessels or biliary ducts. Typically, the vessel path will include vessel branch points at which the path may follow either a relatively larger-diameter, higher-flow branch vessel, or a relatively smaller, lower-flow branch vessel.
Heretofore, three general types of catheters have been developed for accessing internal target sites. One type is a torqueable catheter having relatively rigid tube construction and large-diameter lumen. in particular, the catheter tube may be formed as a braided fiber or wire laminate which has high torque properties. The distal portion of the catheter can be made narrower and more flexible by eliminating laminate windings or braid from this portion of the catheter, but this compromises torque transmission. Torqueable catheters of this type are generally too large in diameter and too rigid to be safely advanced through narrow, tortuous vessel or duct paths.
Another type of guidable catheter is a guide-wire catheter which contains a single-lumen catheter used in conjunction with a flexible, torqueable, guide wire which can be moved slidable within the catheter. In a typical catheter-placement operation, the wire is advanced along the vessel pathway, using wire torquing to orient the somewhat bent tip of the wire along the selected path, i.e., into and through selected branch vessels and/or regions of sharp bends. The catheter is then advanced along the wire with the wire held in place. The wire and catheter are alternately advanced in this manner until the target site is reached. Thereafter, the wire can be removed to allow fluid delivery through the catheter into the site. Since the wire can be both torqueable and quite flexible, and the catheter can be a thin-walled flexible tube, the catheter device is well suited for accessing sites via small-diameter tortuous paths.
Another general class of guidable catheters have a distal-end balloon which can be partially inflated to carry the catheter in the direction of highest blood flow, and therefore along a vessel path having maximum blood flow. The balloon may be further inflated, at a selected target site, for purposes of occluding blood flow, or for anchoring the catheter end at the selected site. Extending the balloon to contact the walls of a blood vessel can also be useful in relaxing spasmodic vessel muscles, resulting in less vessel constriction. Balloon catheters thus have the advantage over guide-wire catheters in that they can take advantage of blood flow for advancing along a vessel pathway, and various advantages relating to balloon contact with vessel walls can be achieved.
In one construction, the balloon catheter has a double-lumen construction, where one lumen communicates with the distal balloon, for transferring fluid to or from the balloon. The second lumen allows delivery of injected material, such as radio-opaque tracer material or therapeutic agent, into the target site. One advantage of the double-lumen catheter is the ability to inflate the balloon to relatively high pressure, which is particularly useful when the balloon is used for stretching a vessel wall, in a catheter treatment for removing vessel plaque. Also, the catheter can be firmly anchored at the target site when the balloon is in a highly inflated state. The double-lumen balloon catheter, however, is not well suited for guidance along small-diameter, tortuous pathways, since the catheter typically has a relatively large outer shaft diameter, and these shafts are generally relatively inflexible. Alternatively, the two catheter lumens may be made relatively small, but here fluid passage through the lumens is slow and limited to low-viscosity agents. Also, since the catheter is guided by blood flow, the device is limited in use to vessel paths with highest blood flow.
In a second balloon-catheter construction, the catheter has a single-lumen tube which communicates with a slow-leak balloon to the distal tube end. In operation, fluid is supplied through the tube at a slow controlled rate, to maintain the balloon at an inflated condition which promotes fluid-directed movement through the vessel path. The single lumen tube can have a small-diameter, highly flexible construction which permits movement along a small-diameter, tortuous vessel path. The ability to guide the catheter, however, is limited to vessel or duct branches with greater flow, as above, so the catheter is not generally useful for accessing a site against the direction of flow, or along a pathway which includes relatively low-flow branches. Another limitation of the single-lumen catheter is that the slow-leak principle of balloon inflation does not allow for high balloon pressures, and therefore the catheter would not be useful, for example, in stretching a vessel for purposes of plaque removal. By the same token, since fluid released from the balloon is somewhat slow, the catheter is not well-suited to delivery of fluid material rapidly at the target site.
A third balloon catheter construction has a single-lumen catheter which communicates with a sealed balloon. The catheter is able to access small-vessel tortuous paths and allows relatively high balloon inflation pressures. The catheter is limited, however, to vessel paths of highest blood flow, and of course cannot be used to deliver fluid to the target site.